1. Field of the Invention
The invention is directed to an improved armature for an electrical machine.
2. Description of the Prior Art
From U.S. Pat. No. 4,886,392, a rotor with a shaft that has a knurled feature and smooth regions on a surface of the shaft is already known; the shaft has approximately the same external diameter both in the region of the knurled feature and in the smooth regions. The rotor, which is slipped onto the shaft, however, has no taper in the internal diameter, which is disposed in the region of the knurled feature.
From U.S. Pat. No. 5,625,511, a stator with a shaft is known, in the middle of which shaft a knurled feature is provided. On the far side of the knurled feature on the shaft there is a smooth region, which has the same external diameter as the knurled feature and can be used to guide the stator, which is secured on the shaft. The stator, however, has no taper in the internal diameter, which is disposed in the region of the knurled feature.
From the book entitled xe2x80x9cFeinmechanische Bauelementexe2x80x9d [xe2x80x9cPrecision-Mechanical Componentsxe2x80x9d] by Prof. Dr.-Ing. S. Hildebrandt, Carl Hanser Verlag, Munich, page 221, it is known to use a shaft with a knurled feature; the knurled feature has an external diameter larger than an internal diameter of a component that is slipped onto the shaft in the region of the knurled feature and secured there. The component is mechanically softer than the shaft and presses into the knurled feature of the shaft, resulting in a reinforcement by positive engagement. Outside the knurled feature, the external diameter of the shaft is smaller than the internal diameter of the component.
U.S. Pat. No. 4,339,873 shows a rotor shaft that has an indentation in which a knurled feature is disposed. The component that is slipped onto the rotor shaft is disposed with its taper in the region of the knurled feature, in the installed state. The taper, however, is created by plastic deformation of the component, after the component has been slipped onto the shaft.
The armature of the invention has the advantage over the prior art that in a simple way, a component can be mounted on a shaft and securely held. Also, because of the protrusion in the internal diameter of the component, the material of the component deforms plastically in the region of the protrusion and flows into the knurled feature and thus develops a positive engagement.
For the component, a plastic injection-molded magnet can advantageously be used, since this magnet is mechanically softer than the shaft.
It is also advantageous that the protrusion is disposed centrally in the component, because as a result the stresses can decrease uniformly all the way around the knurled feature.